Helical slow wave structure traveling wave tube having attenuation material coating the inside of the hollow support members



y 1967 H. J. LANDSBERGEN 3,329,855

HELICAL SLOW WAVE STRUCTURE TRAVELING WAVE TUBE HAVING ATTENUATION MATERIAL COATING THE INSIDE OF THE HOLLOW SUPPORT MEMBERS Filed Sept. 20, 1963 JJUPPO/QT 200 m/ m e JM M.

INVENTOR. Hf/VO/WC'MS a ulvosaifiw- Le/JA Air-roe!!! United States Patent M HELICAL SLOW WAVE STRUCTURE TRAVELING WAVE TUBE HAVING ATTENUATION MATE- RIAL COATING THE INSIDE OF THE HOLLOW SUPPORT MEMBERS Hendricus Johannes Landsbergen, Palo Alto, Calif., as-

signor to the United States of America as represented by the Secretary of the Air Force Filed Sept. 20, 1963, Ser. No. 310,512 2 Claims. (Cl. SIS-3.5)

This invention relates to improvements in traveling wave tubes and more particularly to an attenuator for a traveling Wave tube and the method of manufacturing the same.

Traveling wave tubes and other electron discharge devices are employed in a large number of applications and are particularly suited for use in amplifying radio energy over a wide band of frequencies. Most conventional traveling wave tubes employed as amplifiers include an element in elongated form, usually a helix, for transmission and amplification of electromagnetic energy passing therethrough. The helical element is adapted by construction and arrangement to conduct an electromagnetic wave along a helical path at approximately the same velocity as an associated electron beam passing through the axis of the helix. Amplification is achieved by the interaction between the electron beam and the electromagnetic waves and, sincet-he amplification of the tube depends on the fact that the wave and electrons are traveling at the same velocity, it can be seen that any unbalance will affect the operation of the tube.

In the use of traveling wave tube amplifiers, unwanted self-sustaining oscillations are often generated by reflections and impulses in the magnetic field surrounding the helix. These oscillations are generally caused by impedance mismatches between the output and load circuits and effectively operate to limit the useful range of amplification by causing the device to become unstable when used in a high gain system. Many attempts have been made to reduce these undesirable effects, such as, surrounding or coating the helix itself, or providing attenuating material as coating for the support elements.

Accordingly, it is an object of the invention to provide an improved device constructed in a new way to minimize the effect of these reflections and eliminate as far as possible unwanted oscillation caused by such energy reflections.

A further object of the invention is to provide a novel attenuator device which is conducive to maintaining high etficiency of operation, and wherein the attenuator material is protected from damage during assembling and operation of the tube.

A still further object of the invention is the provision of a method of manufacturing the device described above.

A still further object of the invention is the provision of a traveling Wave tube having a series of elements which serve the dual purpose of supporting the helix along its length and attenuating the electric field surrounding the helix.

A still further object of the invention is the provision of a traveling wave tube wherein the inner wall of hollow elongated cylindrical support members is coated with attenuating material.

These and other advantages, features and objects of the invention will become more apparent from the following 3,329,855 Patented July 4, 1967 description taken in conjunction with the illustrative embodiment in the accompanying drawing, wherein:

FIGURE 1 is a perspective view of a portion of a traveling wave tube with the envelope broken away to show the internal operating elements.

FIGURE 2 is a detail sectional view of one of the attenuator elements.

Referring more in detail to the drawing, the numeral 10 indicates the traveling wave tube envelope. An electron beam is concentrated and guided along in an axial direction through a helical slow wave structure 12. A corresponding electromagnetic wave travels at substantially the same velocity and along the helix. The envelope is provided with standard input and output terminals (not shown).

A series of attenuation units comprising non-conducting tubular members 14 extend along the inner wall of envelope 10 and also function as supports for the helix 12. Unique to the present invention is the feature of support rods 14 which serve the additional purpose of attenuators for absorbing the unwanted reflections and oscillations referred to above. The supporting and attenuating elements are of a special construction designed for reducing these adverse effects. In addition, the attenuating material is located inside the tubular members 14 thus protecting it from damage during handling, assembling and operation. In the embodiment disclosed, three such attenuating elements 14 are spaced at positions around the outer circumference of the helix 12. Each element comprises an elongated hollow tube on the interior surface of which a coating of suitable attenuating material such as carbon in graphite form 16 or other resistive material has been deposited. The elements 14 are made of quartz, ceramic, or other dielectric material.

In the process of manufacturing, the first step comprises coating or otherwise depositing carbon or other suitable attenuating material on the interior surface of a dielectric tubular member. This coated surface is then further protected by evacuating the atmosphere from within the tubular member. Alternatively, after evacuation, the attenuator units 14 may be charged with an inert gas, preferably at atmospheric pressure or lower. This design has the advantage that the attenuator material is not exposed to adverse atmospheres in the course of the subsequent processing, assembling, and operation of the traveling wave device.

Each attenuator 14 is sealed off at each end when the evacuation or the gas filling operation has ben completed. These attenuator elements 14 incorporated in traveling wave tubes have been found uniquely effective in reducing the unwanted effects described above.

This construction has the added advantage that the attenuator material is not exposed to adverse and damaging conditions in the process of further construction of the traveling wave tube.

It should be understood that the form of my invention shown and described herein is to be taken as a preferred embodiment of the same and it will be apparent that various changes in construction, including shape, size, and arrangement of the parts may be made without departing from the true spirit and scope of the invention.

What is claimed is:

1. In a traveling wave tube, a slow wave structure of helical formation for transmitting signals, a plurality of attenuating units for said helical member, said units extending axially and placed in supportive relationship to said helical member and comprising evacuated tubing members of low-loss dielectric material, and a coating of attenuator material on the inside surfaces of said tubing members.

2. A traveling Wave tube comprising a tubular envelope, a slow Wave structure of helical configuration located Within said envelope, a plurality of hollow tubular attenuating elements extending axially within said envelope and so located with respect to the outside diameter of the helical slow wave structure as to function also as supports for said slow wave structure, and a deposition of attenuating material located on the interior surface of said hollow tubular elements.

References Cited UNITED STATES PATENTS 2,942,331 6/1960 Smiley 29155.7

ELI LIEBERMAN, Primary Examiner.

1O HERMAN KARL SAALBACH, Examiner.

\P. L. GENSLER, Assistant Examiner. 

1. IN A TRAVELING WAVE TUBE, A SLOW WAVE STRUCTURE OF HELICAL FORMATION FOR TRANSMITTING SIGNALS, A PLURALITY OF ATTENUATING UNITS FOR SAID HELICAL MEMBER, SAID UNITS EXTENDING AXIALLY AND PLACED IN SUPPORTIVE RELATIONSHIP TO SAID HELICAL MEMBER AND COMPRISING EVACUATED TUBING MEMBERS OF LOW-LOSS DIELECTRIC MATERIAL, AND A COATING OF AT- 